1. Field of the Invention
The present invention is related to a U-shaped multi-frequency antenna of high efficiency, and especially to a monopole antenna particularly suitable for use in wireless local area networks (WLAN), it is an omni-directional multi-frequency antenna with a high gain and a bandwidth convenient for manufacturing.
2. Description of the Prior Art
Wireless communication keeps on fast growing in the fields including mobile phones, wireless Internet and wireless household electrical appliances; wireless local area networks (WLAN) are also included in the wireless networks.
The main bandwidths of WLAN used in the industry of scientific and medical (ISM) are 2.4-2.4835 GHz, 5.15-5.35 GHz and 5.725-5.825 GHz. Hence the antennas used in such a WLAN system must be able to handle more than two kinds of related bandwidths. Moreover, design of antennas of the WLAN system also include the consideration of larger bandwidths required, and the feature of simple impedance matching with a feed line.